Hydroxy-pendent benzoxazole copolymers

ABSTRACT

Alcohol-soluble, aromatic heterocyclic copolymers having repeating units of the formula: ##STR1## wherein x has a value of 0.10 to 0.90 and y has a value of 1.0-x. These copolymers are useful in the preparation of organic/inorganic hybrid materials having transparency which comprise the sol-gel derived, hydrolytically condensed reaction product of a metal alkoxide of the formula M(OR) w  wherein R is a lower alkyl group, M is Si, Ti, Al or a mixture thereof, and w is the valence value of M, and the above copolymer.

RIGHTS OF THE GOVERNMENT

The invention described herein may be manufactured and used by or forthe Government of the United States for all governmental purposeswithout the payment of any royalty.

BACKGROUND OF THE INVENTION

The present invention is directed to heterocyclic copolymers,particularly benzoxazole copolymer systems containing pendent hydroxylgroups.

Sol-gel processing of ceramics and glass is an area of intense researchinterest because of inherent advantages compared to more conventionalprocessing. By starting with well mixed solutions or sols, chemicalhomogeneity even on the molecular scale can be obtained.

A great variety of metal alkoxides are commercially available. Stillothers have been synthesized for specific uses. The alkoxides areutilized by first partially hydrolyzing the alkoxide,

    M(OR).sub.v +wH.sub.2 O→M(OR).sub.v-w (OH).sub.w +wROH

where R represents a lower alkyl group and M represents Si, Ti, Al andthe like, as well as mixtures thereof. The partially hydrolyzed speciesare then allowed to link forming M--O--M bonds by a polymerization orcondensation reaction.

The majority of work done on sol-gel of polymerized alkoxides has beendone for glasses. Much of this centers around SiO₂ glasses or high SiO₂glasses. The growing use of optical fibers for transmission ofinformation at high rates has provided an incentive to seek fabricationmethods for optical grade SiO₂ glass which is less expensive than vaporphase methods. Further, silicon alkoxides exist which are inexpensive,highly pure and easily polymerized to gels. The most common of these istetraethylorthosilicate (TEOS), Si(C₂ H₅ O)₄, the ethoxide of silicon.When an alcohol (e.g., ethanol) is used as a mutual solvent, TEOS can bemixed with water. This mixture is slow to hydrolyze, but the rate can beincreased by additions of acids or bases as catalysts. Acid catalyzedgels form transparent gels which appear to be rather uniform polymers.Base catalyzed gels are not as transparent and are thought to containSiO₂ clusters which then link together to form a gel.

In the case of TEOS, the mechanism for gel formation is polymerizationafter partial hydrolysis of Si(C₂ H₅ O)₄ to have both ethyl groups andhydroxide groups attached to the Si:

    Si(C.sub.2 H.sub.5 O).sub.4 +wH.sub.2 O→Si(C.sub.2 H.sub.5 O).sub.4-w (OH).sub.w +wC.sub.2 H.sub.5 OH

Reaction of an OH group on one Si with a C₂ H₅ O group on anotherreleases another alcohol molecule and forms a siloxane bond, Si--O--Si,at all temperatures close to ambient. These siloxane bonds form thebasis for the polymerization and thus the gelation.

Such gels contain large amounts of water and alcohol, leaving a lowdensity of SiO₂. Drying such gels results in large shrinkages asliquid-filled pores partially collapse. Since the liquid content of thegel is large and the pores are small, liquid transport is slow and rapiddrying leads to large shrinkages near the gel body surfaces. Because themechanical strength of the gel is low, these non-uniform shrinkages leadto cracking.

Several studies have demonstrated the successful incorporation ofvarious functionalized oligomers into a sol-gel network to produce novelorganic/hybrid materials referred to as `ceramers`. Such studies haveinvolved, for example, a sol-gel reaction using tetramethylorthosilicate(TMOS) or TEOS and silanol-terminated poly(dimethylsiloxane). Othersystems investigated were hybrids based upon TEOS or TMOS, or relatedmetal alkoxides, reacted with an oligomer of poly(tetramethylene oxide)endcapped with isocyanatopropyltriethoxysilane. Wilkes et al, U.S. Pat.No. 5,316,695, disclose the use of a polymeric catalyst, such aspoly(styrenesulfonic acid), in such a system.

Organic/inorganic hybrid materials prepared through sol-gel processinghave the potential to possess the desired properties of both organic andinorganic components, such as high tensile modulus, scratch resistance,thermal and dimensional stability from the inorganic network, as well astoughness, flexibility and light weight from the organic portion. Avariety of high performance, thermally stable polymeric structures areknown, but they are intractable and virtually impossible to process.Aromatic heterocyclic polymers are the most attractive high temperature,high performance polymer systems. Although these polymers have excellenthigh temperature properties, they exhibit solubility only in highboiling aprotic or acidic solvents.

Accordingly, it is an object of the present invention to providearomatic heterocyclic polymers having improved solubility properties.

It is another object of the present invention to provide aromaticheterocyclic polymers having functionality for co-reaction with metalalkoxides for preparing ceramers.

Other objects and advantages of the present invention will be apparentto those skilled in the art.

SUMMARY OF THE INVENTION

In accordance with the present invention there are provided aromaticheterocyclic copolymers of the formula: ##STR2## wherein x has a valueof 0.10 to 0.90 and y has a value of 1.0-x.

This copolymer is derived from the polycondensation of5-hydroxyisophthalic acid, 4,4'-oxybisbenzoic acid and4,4'-[2,2,2-trifluoro- 1(trifluoromethyl)ethylidene]bis[2-aminophenol]dihydrochloride, as shown below. Briefly, the polymerization processcomprises the following steps: (i) dehydrochlorination of thediamino-diol dihydrochloride in the presence of the dicarboxylic acidmonomers in 77% polyphosphoric acid (PPA); (ii) addition of P₂ O₅ toraise the P₂ O₅ content of the medium to 82-84%; (iii) chain propagationand cyclodehydration; and (iv) precipitation of the polymer into water,followed by washing and drying the polymer. Step iii may be carried outat a temperature of about 160° to 190° C. for about 4 to 64 hours. It isgenerally preferred to carry out the polymerization in step-wisefashion, for example, heat to 165° C. over a period of 2-4 hours, 165°C. for 16 hours, then 172° C. for 48 hours. The overall polymerizationreaction is: ##STR3##

The organic/inorganic hybrid materials can be prepared by a number ofdifferent methods including, for example, the combination of thehydroxy-pendent benzoxazole copolymers of this invention with TMOS, asillustrated hereinafter. The ratio, by weight, of organic polymer to themetal alkoxide can range from 1:9 to 9:1.

Generally, there is initially prepared a solution of the hydroxy-pendentbenzoxazole copolymer in a suitable solvent at a concentration of about1 to 10 percent (weight/volume), preferably about 6-8 percent.Generally, suitable solvents are aprotic solvents, such as THF, DMAC andthe like. To this solution is added a measured amount of water and TMOSat a mole ratio (water:TMOS) of 3.0:1 to 3.5:1. The resulting mixture isstirred until an homogeneous solution is obtained. Coupling orcrosslinking between the organic and inorganic polymers is promoted bythe addition of a coupling agent to this mixture. Suitable couplingagents contain groups which can react with both the organic polymer andthe inorganic polymer, for example, isocyanopropyltriethoxysilane,isocyanopropyltrimethoxysilane, gamma-aminopropyltrimethoxysilane orgamma-aminopropyltriethoxysilane. The coupling agent is used in anamount of about 1 to 15 mol %, preferably about 5 to 10 mol %, based onthe inorganic polymer-forming compound.

Thereafter, the resulting semigel, in one embodiment of the invention,can be formed into a thin film by known methods, such as vacuumevaporation, or applied to a supporting substrate. Alternatively, it canbe cast into a suitable mold, dried slowly over a period of 8 to 200hours at room temperature, then dried under vacuum for 8 to 48 hours at80°-100° C.

The following examples illustrate the invention:

EXAMPLE I Copolymer Preparation (25:75)

Into a resin flask equipped with a mechanical stirrer, nitrogen inletand outlet, were placed 4, 4'-dicarboxybiphenylether (3.87 g, 15 mmol),5-hydroxyisophthalic acid (0.91 g, 5 mmol), 4,4'-(2,2,2-trifiuoro-1-(trifiuoromethyl)ethylidene)bis(2-aminophenol)(7.32 g, 20 mmol) (available from Daychem Labs, Inc. Dayton Ohio) andpolyphosphoric acid (PPA, 115%, 90.3 g). The reaction mixture was heatedat 135° C. for 21/2 hours under nitrogen at reduced pressure to removeair. The mixture was cooled to 120° C. and 9.1 g of 99.9% phosphoruspentoxide (P₂ O₅) was added. The mixture was then heated from 120° C. to165° C. over a period of 11/2 hours, held at 165° C. for 16 hours, thenheated to 172° C. for 48 hours. After cooling to 100° C., a mixture of85 g of 85 % phosphoric acid and 15 g of water was added, and themixture was stirred overnight at 70° C. to give an homogeneous solution.The reaction mixture was poured into water to precipitate the copolymer.The precipitated copolymer was chopped in a high speed blender, thenthoroughly washed with hot water, filtered and dried. A copolymer with(η)=1.02 dL/g (methanesulfonic acid, 30° C.) was obtained inquantitative yield.

EXAMPLE II Copolymer Preparation (40:60)

Into a resin flask equipped with a mechanical stirrer, nitrogen inletand outlet, were placed 4, 4'-dicarboxybiphenylether (3.4056 g, 13.2mmol), 5-hydroxyisophthalic acid (1.6016 g, 8.8 mmol), 4,4'-(2,2,2-trifluoro-1-(trifluoromethyl)ethylidene)bis(2-aminophenol)(8.052 g, 22 mmol) and polyphosphoric acid (PPA, 115%, 97.1 g) . Thereaction mixture was heated at 130° C. for 21/2 hours under nitrogen atreduced pressure to remove air. The mixture was cooled to 120° C. and9.88 g of 99.9% phosphorus pentoxide (P₂ O₅) was added. The mixture wasthen heated to 150° C. over a period of 2 hours, then heated to 175° C.for 64 hours. After cooling to 100° C., a mixture of 65 g of 85%phosphoric acid and 20 g of water was added, and the mixture was stirredovernight at 70° C. to give an homogeneous solution. The reactionmixture was poured into water to precipitate the copolymer. Theprecipitated copolymer was chopped in a high speed blender, thenthoroughly washed with hot water, filtered and dried. A copolymer with(η)=1.34 dL/g (methanesulfonic acid, 30° C.) was obtained inquantitative yield.

EXAMPLE III Preparation of Organic/Inorganic Hybrid Material I

0.2 g of the copolymer of Example I was dissolved in 2.8 ml of anhydrousTHF. 0.01 ml of triethylamine, 0.08 ml of water and 0.25 g oftetramethoxysilane were then added to the copolymer/THF solution. Theresulting mixture was stirred overnight at room temperature. Theresulting viscous homogeneous solution was transferred to a Petri dishand dried slowly over a period of 24 hours. The resulting film was driedunder vacuum for 24 hours at 80° C. A crack-free, transparent, thickfilm was obtained.

EXAMPLE IV Preparation of Organic/Inorganic Hybrid Material II

0.16 g of the copolymer of Example II was dissolved in 2.2 ml ofanhydrous THF. 0.008 ml of triethylamine, 0.075 ml of water and 0.20 gof tetramethoxysilane were then added to the copolymer/THF solution. Theresulting mixture was stirred overnight at room temperature. Theresulting viscous homogeneous solution was transferred to a Petri dishand dried slowly over a period of 24 hours. The resulting film was driedunder vacuum for 24 hours at 80° C. A crack-free, transparent, thickfilm was obtained.

Various modifications may be made in the instant invention withoutdeparting from the spirit and scope of the appended claims.

We claim:
 1. An aromatic heterocyclic copolymer having repeating unitsof the formula: ##STR4## wherein x has a value of 0.10 to 0.90 and y hasa value of 1.0-x.
 2. The copolymer of claim 1 wherein x is 0.25 and y is0.75.
 3. The copolymer of claim 1 wherein x is 0.40 and y is 0.60.
 4. Anorganic/inorganic hybrid material having transparency which comprisesthe sol-gel derived, hydrolytically condensed reaction product of ametal alkoxide of the formula M(OR)_(w) wherein R is CH₃ or --C₂ H₅, Mis Si, Ti, Al or a mixture thereof, and w is the valence value of M, anda copolymer having repeating units of the formula: ##STR5## wherein xhas a value of 0.10 to 0.90 and y has a value of 1.0-x.
 5. The hybridmaterial of claim 4 wherein the weight ratio of said copolymer to saidmetal alkoxide is in the range of 1:9 to 9:1.
 6. The hybrid material ofclaim 4 further comprising about 1 to 15 mol % of a silane couplingagent.
 7. The hybrid material of claim 6 wherein said coupling agent isselected from the group consisting of isocyanopropyltriethoxysilane,isocyanopropyltrimethoxysilane, gamma-aminopropyltrimethoxysilane andgamma-aminopropyltriethoxysilane.
 8. The hybrid material of claim 4wherein said metal alkoxide is tetramethoxysilane.